(a) Technical Field
The present invention relates to a novel photopolymerizable monomer having at least one unsaturated double bond and epoxide, and a photocurable composition comprising the photopolymerizable monomer and an initiator.
(b) Background Art
Monomers having unsaturated double bonds are easily polymerizable with light or heat, and are highly sensitive to light.
Photocurable compositions are cured by light to form solid or highly viscous films. Therefore, they are used in the manufacture of protective films, surface coatings, electrolyte permeable/non-permeable films, functional films for electronic devices, recording films, and the like.
In general, a photopolymer, wherein the degree of polymerization becomes different depending on the intensity of light irradiation, comprises an acryl or epoxy monomer, an initiator and a polymer binder. Acryl based films are widely applicable, but tend to experience severe shrinkage upon curing by light or heat. In contrast, epoxy based films experience less shrinkage, but have low reactivity. Various photopolymerizable compositions have been developed to solve this problem.
For instance, Korean Patent Publication No. 1992-4550 discloses a photopolymerizable composition comprising a) a polymerizable binder, b) a free radical polymerizable compound having at least one terminal ethylenic double bond, and c) an N-heterocyclic compound, a thioxanthone derivative and a dialkylamino compound as photoinitiator.
And, Korean Patent Publication Nos. 1991-17382, 1991-1467, 1990-3685, 1990-3685, 1989-10615 and 1988-11262, and US Patent Application No. 08/698,142 disclose photopolymerizable compositions comprising acrylates or alkacrylates of polyalcohols as main components together with liquid monomers such as free radical polymerizable acrylate ester.
However, these compositions are accompanied by the problem that shrinkage occurs during the polymerization of the monomers, thereby causing trouble in deciphering the recorded information.
To solve these problems, Waldman et al. used cationic epoxy polymerization to form holograms, and, because epoxy polymerization involves opening of the epoxide monomer rings, the polymerization exhibits about half as much shrinkage as acrylate polymerizations [Waldman et al., “Cationic Ring-Opening Photopolymerization Methods for Volume Hologram Recording”, SPIE vol. 2689, 1996, 127]. It has further been proposed that spiro-orthoesters and spiro-orthocarbonates, so-called expanding monomers, be added to epoxy polymerization systems [Expanding Monomers: Synthesis, Characterization, and Applications (R. K. Sadhir and R. M. Luck, eds., 1992) 1-25, 237-260; T. Takata and T. Endo, “Recent Advances in the Development of Expanding Monomers: Synthesis, Polymerization and Volume Change”, Prog. Polym. Sci., Vol. 18, 1993, 839-870]. Such spiro compounds have been reported to exhibit relatively small shrinkage, or even expansion, upon polymerization. And, U.S. Pat. No. 6,221,536 proposes adding a specific spiro compound as expansion agent in order to compensate for the polymerization-induced shrinkage.
However, the shrinkage compensating ability of the spiro compound is not so great because it is caused, at least in part, by a phase change. Also, the rates of ring-opening and accompanying fragmentation side reactions are difficult to tune [C. Bolin et al., “Synthesis and Photoinitiated Cationic Polymerization of 2-methylene-7-phenyl-1,4,6,9-tetraoxaspiro-[4,4]nonane,” Macromolecules, Vol. 29, 1996, 3111-3116].
U.S. Pat. No. 4,842,968 discloses a hologram recording medium comprising a photoimaging material inside a porous glass material. This requires the process of removing the non-exposed region after irradiation of light, which may be accompanied by such problems as diffusion of solvent, unwanted chemical reaction, difficulty of removing unreacted monomers, and so forth.
U.S. Pat. No. 6,268,089 discloses a photorecording medium comprising a hybrid inorganic-organic matrix comprising a metallic element, e.g., silicon, titanium, germanium, zirconium, vanadium and aluminum, suitable for use in holographic storage systems. According to the process for holography of the invention, the photopolymerization of the precursor of the hybrid inorganic-organic matrix and the photochemical reaction of monomers by which holographic recording is carried out are independent of each other. As a result, the process of removing unreacted monomers can be eliminated, and improved thermal, mechanical and chemical stability are obtained through the combination of an oligomer and an oxide.
However, this method has the problem that the efficiency of photorecording may decrease as the photocurable monomers are polymerized during the polymerization of the hybrid inorganic-organic precursor (thermal curing).
The information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.